Both terrestrial radio broadcasters (primarily AM and FM stations) and satellite radio broadcasters (Sirius Satellite Radio and XM Satellite Radio) suffer from annoying signal dropouts. Satellite radio uses coding to allow a signal dropout of approximately four seconds without any loss of audio output, for example when a car radio passes under an overpass at high speed and cannot see the satellite for less than four seconds. But even with this coding, longer signal dropouts produce annoying silences until the signal is regained. In some areas, such as highly mountainous terrain, signal dropouts make satellite radio unusable. The present invention uses memory to greatly reduce the annoyance of signal dropouts.
The use of memory at a receiver is well known in the art. DirectTV, for example, offers a TiVo equipped satellite television receiver, which can store programs on a hard drive and play them back at a later time. In U.S. Pat. No. 6,785,656 “Method and apparatus for digital audio playback using local stored content” Patsiokas et al describe a similar system for use with satellite radio. Since TiVo and its competitors are called PVR's (Personal Video Recorders), Patsiokas' invention might be called a PAR (Personal Audio Recorder).
In U.S. Pat. No. 6,564,003 Marko et al describe another use of memory with satellite radio. Marko demodulates the bit stream from a broadcaster, such as XM Satellite Radio, and records it on a memory medium (e.g., a recordable CD) for later playback at a location that either cannot receive the satellite signal or does not need real time reception. As in Patsiokas, the selection of the recorded program to be played back is subscriber controlled.
In US Patent Application 2004/0266336 “System and method for providing recording and playback of digital media content” Patsiokas et al describe a system for recording and time-shifting a broadcast so that the subscriber does not experience signal dropouts when a real-time signal is not available. Sirius has announced a product, its S50 radio, which stores up to 50 hours of one or more Sirius Radio channels. In US Patent Application 2003/0129941 Kawamata et al buffer past signals to allow switch over to stored content when the signal is lost. The substituted content can be based on subscriber preferences.
The use of memory in satellite radio receivers is also dealt with by Marko et al in U.S. Pat. No. 6,834,156 “Method and apparatus for controlling user access and decryption of locally stored content at receivers in a digital broadcast system,” U.S. patent application Ser. No. 09/695,226 for “Method and Apparatus for Employing Stored Content at Receivers to Improve Efficiency of Broadcast System Bandwidth Use,” in U.S. patent application Ser. No. 09/695,228 for “Method and Apparatus for Implementing File Transfers to Receivers in a Digital Broadcast System,” and in U.S. Pat. No. 6,834,835 for “Method and Apparatus for Providing On-Demand Access of Stored Content at a Receiver in a Digital Broadcast System.”
In US Patent Application 2004/0225519 Martin describes storing a library of multimedia works on a storage device and playing a selection based on subscriber preferences.
In U.S. Pat. No. 6,697,608 “Digital audio/visual receiver with recordable memory” King-Smith describes a broadcast receiver with memory to give the subscriber a wider selection of content.
In US Patent Application 2004/0083487 Collens et al describe a media distribution system which delivers content to a subscriber in encrypted form and then delivers keys to unlock the content on a specific playback device.
In U.S. Pat. No. 6,289,455 “Method and apparatus for preventing piracy of digital content” Kocher et al describe a secure CryptoFirewall which protects critical portions of memory so that cryptographic keys used by a cryptoprocessor are inaccessible to all other parts of the system. These keys are made inaccessible to avoid the danger of a pirate attempting to learn them, creating a CryptoFirewall in Kocher's terminology. This architecture prevents the frequent error in the implementation of cryptograpic systems of storing keys in normal read-write memory where the keys are potentially accessible to piracy. The thinking behind this frequent error is that keys need to be written when entered and read when used for encryption or decryption. While this is true, allowing keys to be read by parts of the system which have no need for them other than for piracy, is extremely dangerous. Kocher, however, is not concerned with signal dropouts.
In contrast to the prior art, the present invention:                automatically determines when to record content, which content to record, when to access stored content, and which stored content is accessed, with little or no subscriber input;        automatically checks each content segment to ensure it is dropout-free, keeps only dropout-free content segments in memory (or marks recorded content with dropouts for use only in unusual circumstances), and thereby ensures that playback of recorded content is dropout-free (or as dropout-free as possible);        automatically determines when recorded content is appropriate (e.g., when the program material is recorded music) and, if so, uses dropout-free recorded content segments in preference to real-time broadcast segments, buffering real-time broadcast segments to ensure they are dropout-free before presenting them to the subscriber.        automatically determines when recorded content is not appropriate (e.g., when the program requested is a real-time sporting event), and if so, and uses real-time broadcast segments.        